In a missile attack, a single missile, multiple missiles or a missile with multiple warheads may be launched against a variety of targets, with the missile coming in from space such that, in order to reach its targets, it or its re-entry vehicle or vehicles must re-enter the atmosphere with sufficient protection to prevent disintegration.
In order to countermeasure such incoming missiles and their warheads, it has been proposed to send up a kill vehicle that is designed to directly impact a re-entry vehicle to disable it, either by a direct hit or by altering its trajectory. While in the past projected solutions have included the use of nuclear weapons in space, the obvious disadvantage is the production of radiation. Moreover, rejected solutions include providing conventional explosives aboard a kill vehicle, with proximity fuses to detonate in the vicinity of a re-entry vehicle. The reason that this approach has been rejected is that insufficient energy is available to assure the destruction of the re-entry vehicle and the precise timing required to be effective given the large closing velocity.
As currently deployed to counteract incoming intercontinental ballistic missiles, a single kill vehicle is used to counteract a single re-entry vehicle. However, this type of ICBM countermeasure is ineffectual when decoys or multiple warheads are involved.
More importantly, in order to be able to locate and guide a kill vehicle towards a re-entry vehicle, in the past only infrared sensors have been used to track the re-entry vehicle. In so doing, a carrier vehicle picks up a number of objects in a target cloud, tracks them in the IR and tries to determine the point in space where the objects exist. Upon such determination, the carrier vehicle launches multiple miniature kill vehicles, each with there own IR sensor, to intercept the objects.
The problem with a total infrared solution is first and foremost that the objects themselves are only detectable from 10 to 30 kilometers away for small aperture, low cost IR sensors. This being the case, in order to effectively launch a counterattack on incoming missiles, one must expend large amounts of fuel for midcourse corrections to maneuver the miniature kill vehicles launched from the carrier vehicle. Because of the relatively short range of the IR detectors, these midcourse corrections can only be made when the kill vehicle is relatively close to its intended target. Late-in-the-game midcourse corrections require the expenditure of a considerable amount of fuel for the thrusters on the miniature kill vehicles that in turn limits payload size or the number of kill vehicles carried by the carrier vehicle.
Moreover, utilizing a total IR system, it is virtually impossible to hand off a very complex series of objects to a set of interceptors and to know that one has a one-to-one correlation. This means that it is difficult to hand off one particular object to one particular interceptor or kill vehicle. The inability to provide a one-to-one correlation between kill vehicles and objects means that a unacceptable number of kill vehicles will miss a particular object because they are directed to the wrong target.
Presently there are means for distinguishing between re-entry vehicles and decoys so that the probability of a kill vehicle intercepting a re-entry vehicle can be maximized. Thus it is possible to categorize the type of objects in a target cloud and to provide an estimate of the likelihood that a particular object is an armed re-entry vehicle.
It will be seen that if a target cloud includes as many as 50 objects, one may not have 50 kill vehicles aboard a carrier vehicle. One therefore has to avoid intercepting decoys or those objects having a low probability of being an armed re-entry vehicle.
Moreover, if a carrier vehicle carries 30 miniature kill vehicles, it may be necessary to deploy multiple carrier vehicles, each with 30 interceptors or kill vehicles, towards a target cloud.
The problem with multiple targets is that one usually wants to assign one kill vehicle to a target. One also wants to avoid targeting decoys. Further, one usually wants to avoid assigning multiple kill vehicles to a single target because it means that other legitimate re-entry vehicles will not be destroyed. Of course, for high-valued targets in a target cloud, there is also the problem of directing multiple kill vehicles to the very high-valued target.
As will be appreciated, not all of the objects in the target cloud are armed re-entry vehicles, with a large number of objects being decoys. The kill vehicle strategy is then to strip out all the decoys so that the next kill vehicle destroys an armed re-entry vehicle. Moreover, if one can identify an armed re-entry vehicle, then one is likely to want to target more than one kill vehicle against the identified re-entry vehicle in order to assure a successful kill.
The important consideration is to be able to effectively assign and direct kill vehicles to particular targets. Currently available discrimination software and algorithms can determine or prioritize objects in the target cloud, but the discrimination is never perfect. Thus one can never determine to a substantial likelihood that the object is an armed re-entry vehicle as opposed to a decoy. Thus, how to get the kill vehicle aimed at the right target is the essential challenge.